Conventionally, power distribution involved producing power at one or more power plants, then routing that power through a system of power cables, to inverters, to loads such as residential homes. Traditionally, distribution from the power plants to the loads includes several highly regulated steps whereby the voltage is sequentially reduced until it enters the residence at a predetermined, standard voltage. Furthermore, power is distributed with a predetermined, standard alternating current (AC) frequency.
Increasingly, power is supplied to power grids from distributed generation (DG) sources. Such DG sources include photovoltaics, solar-thermal systems, wind, biomass, and geothermal power sources, among others. DG sources provide a voltage boost to the grid wherever they are connected. In small quantities, DG sources can reduce the power required of a base load generator such as a power plant. As such, DG is seen as a mechanism for achieving reduced greenhouse gas emissions, and, if implemented properly, a mechanism for reducing load on the electrical grids on which they are deployed.
Conventional power grids are often ill equipped to deal with the ramifications, however, of DG power generation. In areas where DG sources exceed a certain threshold, the power generated by DG sources, either alone or in combination with power provided by a base plant, can exceed the demand for power amongst the loads on that portion of the grid. This can cause so-called “upstream” current flow, away from the DG sources and loads and towards the power plant. Conventional power grids can be damaged by this type of current flow, and often this scenario results in either overvoltage at the area of the grid having DG sources, or disconnection of the DG sources and loads from the grid entirely. The inability of conventional power grids to handle DG in excess of the power draw by nearby loads has caused some areas to throttle the implementation of renewable technologies where the DG sources combined exceed the minimum power usage in that area.
Furthermore, because conventional power grids rely on single (or few) sources to provide power to the grid, managing the frequency of the AC current provided is relatively simple. Conventional grids provide power at a predetermined frequency, and need only contend with the effects that connected loads may have on the signal shape. For these reasons, electronics that draw power from an electrical grid are often required to comply with standards to reduce unwanted effects on the shape of the signal on the power grid, such as harmonics. With the introduction of hundreds or thousands of DG sources, the shape of the power signal can be modified not just by resistive loads, but also by power sources. DG sources that provide power out of phase or do not provide clean sine wave voltages, can degrade the signal of the power supply. The inability of conventional power grids to maintain a clean, sinusoidal power supply with larger contributions from DG sources has caused some areas to throttle implementation of renewable technologies where the DG sources combined exceed a set percentage, for example 15%, of maximum power usage in that area.
It would be desirable to provide systems and methods that could address these issues for a power grid having DG sources.